1. Field of the Invention
This invention relates to a vibration wave motor, and more particularly to the materials of the components of a vibration wave motor.
2. Related Background Art
In recent years, compactness of drive sources has been desired and to this end, vibration wave motors, ultrasonic wave motors or the like have been developed. Such motors include those shown in U.S. Pat. No. 4,513,219 (issued Apr. 23, 1985) and U.S. Pat. No. 4,495,432 (issued Jan. 22, 1985). Such a motor basically comprises a vibratory member in which a vibration wave is generated, and a moving member contacting the vibratory member and frictionally driven by the vibration generated in the vibratory member.
The vibration wave motor is essentially a motor moved by a frictional drive. Accordingly, the output of the vibration wave motor greatly depends on the product .mu.W of a pressure force W which presses the moving member into contact with the vibratory member and the friction coefficient .mu. of the moving member and the vibratory member. If the pressure force W is increased, the output is considered to increase, but if the pressure force W is excessively increased, the bending vibration of the vibratory member will be suppressed and therefore, the force transmitted to the moving member will be reduced and the output of the motor will be reduced. In a motor utilizing a travelling vibration wave, the moving member is deformed by being pressed and follows the bending vibration wave generated in the vibratory member. In such case, the output is greatly reduced. From the above-noted points, with regard to the frictional drive of the vibration wave motor, the pressure force W cannot be made so great. Therefore, it is necessary to obtain a combination of materials of great friction coefficient .mu.. Generally, however, if materials of great friction coefficient .mu. are rubbed against each other, the amount of abrasion in the friction surfaces thereof becomes very great, and when such materials are used in a vibration wave motor, the life of the vibration wave motor will be very short.
A selection of materials is disclosed in Japanese Laid-Open Patent Application No. 200778/1985. In this application, and a combination of tool steel and aluminum is shown, but this combination is considered to be insufficient to lengthen the life of the motor and obtain a high output.